Method of photocell manufacture by simultaneously sintering the photosensitive material and sealing the cell



Apnl 13, 1965 H. w. KUZMINSKI 3,177,576

METHOD OF PHOTOCELL MANUFACTURE BY SIMULTANEOUSLY SINTERING THE PHQTOSENSITIVE MATERIAL AND SEALING THE CELL Filed Aug. 15, 1961 IN V EN TOR.

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ilza/wa/ United States Patent 3,177,576 METHOD OF PHOTOCELL MANUFACTURE BY SIMULTANEOUSLY SINTERING THE PHOTO- SENSITIVE MATERIAL AND SEALING THE CELL Henry W. Kuzminski, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware Filed Aug. 15, 1961, Ser. No. 131,549 5 Claims. (Cl. 29-4713) This invention relates to photoconductive devices. In particular this invention relates to a novel photoconductive cell and method of making the same.

In the prior art, there are certain photoconductive cells which include a photosensitive element comprising a substantially continuous polycrystalline layer of interlocked photoconducting crystals. These devices are normally formed by depositing photoconductive materials, including appropriate activator materials, onto a substrate, then sintering the deposited layer to form a substantially continuous layer of interlocked photoconductive crystals.

The photoconductive materials conventionally used in the photocells as described above are the sufides, selenides, and sulfoselenides of cadmium having incorporated therein activator proportions of chlorides, and copper or silver.

The above described photoconductive layers are deposited on a substrate, then sintered, and a pair of elec trodes are then deposited thereon. When this has been done, the completed subassembly is encased in a moisture proof container to form a photoconductive cell. Each of the electrodes conventionally comprises a plurality of fingers, the fingers of one electrode being interdigitated with the fingers of the other electrode.

The above described photoconductive cells are quite sensitive and have found many uses. Due to the large volume of these cells that are manufactured, an economical method of manufacturing the photocell is desirable.

It is therefore an object of this invention to provide a novel method of manufacturing a photoconductive cell.

It is another object of this invention to provide an improved method of economically manufacturing a photoconductive cell.

These and other objects are accomplished in accordance with this invention by providing a novel method of making a photoconductive cell in which the photoconductive powder is sintered at the same time as the cell is sealed into the moisture proof container.

The invention will be more clearly understood by reference to the accompanying single sheet of drawings wherein:

FIG. 1 is an enlarged inverted sectional view of a photocell made in accordance with this invention; and,

FIG. 2 is a section view of the photocell shown in FIG. 1 taken on the line 22.

Referring now to the drawings, there is shown a photocell 10. The photocell It) comprises a glass substrate 12 through which two lead-in wires or rods 14 extend. The lead-ins 14 are made of any material which will readily seal to the glass substrate 12, e.g. a chrome iron alloy, and are sealed in a vacuum tight relationship through the glass substrate 12. In the alternative, the lead-ins 14 may extend through enlarged apertures 17 in the glass substrate 12 and a sealing frit 13 placed around the lead-ins. The lead-ins are held by a holder which itself holds the frit in place during the heating operation. During the subsequent heating operation, to be described, the frit 13 is melted to flow into the apertures 17 and seal the lead-ins into the substrate 12 as shown in FIG. 1.

On the substrate 12 is deposited a pair of electrodes 16 and 18 respectively. Each of the electrodes 16 and 18 includes a plurality of finger-like elements 20 and 22,

shown more clearly in FIG. 2. The finger-like elements are interdigitated so that a maximum electrode area is available with a minimum amount of electrode materials shading the photo-conductive material from the light. The electrodes 16 and 18, in the pattern shown in FIG. 2, may be made of a material such as gold and may be deposited by evaporating the gold material onto the glass substrate 12 through a suitable mask (not shown).

When the electrodes 16 and 18 have been deposited, photoconductive powder or material 24 may be sprayed onto the electrodes 16 and 18, and onto the glass substrate 12 that is exposed between the electrodes 16 and 18. As shown in the drawing the photoconductive material bridges the gap between electrodes 16 and 18. The photoconductive powder 24 may comprise a material selected from the group consisting of the sulfides, selenides, and the sulfoselenides of cadmium with activator proportions from the group consisting of copper, silver, and chloride. The photoconductive material 24 may be deposited by any conventional means such as spraying, doctor blading, painting or other conventional deposition process. When the photoconductive powder 24 has been deposited, a glass frit 26 is deposited on the peripheral area of the glass substrate 12. When the frit 26 has been thus positioned, a cover 28 is placed over the subassembly of the photoconductive powder and the deposited electrodes and in physical contact with the sealing frit 26, to form a moisture proof container for the photocell 10. The cover 28 may be made of any moisture proof material which will readily seal to the frit 26, e.g. glass. When these steps have been completed, the entire assembly is fired to sensitize the photoconductive powder 24 by sintering the photoconductive material. Also, the firing operation seals the frit 26 to the cover 28 and to the substrate 12 to seal the container. In addition, the firing operation seals the lead-ins 14 into the substrate 12. Thus, only one firing of the photocell 10 is required resulting in an extremely economical method of manufacturing the photocell.

The firing temperatures and time will vary somewhat depending upon the exact composition of the photoconductive material, and the exact composition of the glass frits 13 and 26. An example of a successfully manufactured photocell was one which used a glass substrate 12 and cover 28. The electrodes used were evaporated gold and the photoconductor comprised parts by weight of cadmium sulfide, 5 parts by weight cadmium chloride, and 0.025 part by weight of copper, the entire assembly being then fired at about 550 for about 30 minutes. An example of a sealing glass frit is a ground mixture of 76.2 weight percent of PbO and 23.8 weight percent of B 0 In the embodiment shown, the photocell is exposed to the signal light through the substrate 12. The reason for this is that the sintered photoconductive material is opaque. It should be understood that the photoconductive powder 24 may be deposited first and the electrodes deposited while the photoconductor is still in powder form, for example, by evaporation, the device being then sealed and sintered in one firing operation. In this last embodiment, the direction of exposure should be through the glass cover 28 rather than the substrate 12.

An economical method of manufacturing a photoconductive photocell has been described. Since the photoconductive sintering or sensitizing is done at the same time as the container is sealed, a considerable cost reduction in manufacturing is achieved.

What is claimed is:

l. The method of manufacturing a photocell, comprising the steps of providing two lead-ins extending through a glass substrate, mounting two electrodes in spaced relation on said substrate, each of which is attached to one of said lead-ins, bridging the gap between said electrodes with unsintered photoconductive powder, providing a glass cover member for said substrate and a layer of glass sealing frit between said substrate and said cover member, and simultaneously sintering said powders and sealing said frit to said substrate and said cover member.

2. The method of manufacturing a photocell comprising the steps of providing unsealed lead-ins through a glass substrate, mounting two electrodes in spaced relation on said substrate, bridging the gap between said electrodes with unsintered photoconductive powder, attaching said lead-ins to said electrodes, placing a glass cover over said substrate with a layer of glass sealing frit between said substrate and said cover, and heating to simultaneously sinter said powder, seal said lead-ins strate, positioning a cover member over said powder and in contact with said last-named frit to form an unsealed container, and heating said container to simultaneously sinter said powder and seal said container and lead-ins.

4. The method as in claim 3, wherein said powder is selected from the group consisting of the sulfides, selenides and sulfoselenides of cadminum, with activator proportions of chlorides and copper or silver.

5. The method as in claim 3, wherein said powder consists essentially of cadmium sulfide, and said powder and said frits are sintered at a temperature of about 550 C. for about minutes.

References Cited by the Examiner UNITED STATES PATENTS 2,114,591 4/38 Clark 338-19 2,727,632 12/55 Mack --18 X 2,908,594 10/59 Briggs 338-19 X 2,972,803 2/61 Koury et a1 29155.5 3,035,372 5/62 Mayers 65-43 X 3,040,213 6/62 Byer et a1 29l55.5 X

JOHN F. CAMPBELL, Primary Examiner. 

1. THE METHOD OF MANUFACTURING A PHOTOCELL, COMPRISING THE STEPS OF PROVIDING TWO LEAD-INS EXTENDING THROUGH A GLASS SUBSTRATE, MOUNTING TWO ELECTRODES IN SPACED RELATION ON SAID SUBSTRATE, EACH OF WHICH IS ATTACHED TO ONE OF SAID LEAD-INS, BRIDGING THE GAP BETWEEN SAID ELECSOLIDIFICATION, PLACING SAID CASTING AS THE CORE IN A SECOND MOLD, CASTING METAL INTO THE SECOND MOLD SO AS TO SUR- 